This invention relates generally to fabrication of integrated circuits, and more specifically to formation of oxide isolated epitaxial islands.
Isolation of individual elements found in integrated circuit devices becomes more important and more difficult as integrated circuits increase in complexity. Transistor sizing and spacing are constantly becoming smaller in order to realize increased circuit densities on an integrated circuit chip.
Improved isolation can be obtained if all active devices are isolated by an oxide insulator underneath as well as on all sides. Such complete isolation would eliminate the potential of latchup in CMOS circuits, and decrease parasitic capacitances in all types of active devices. In addition, total oxide isolation would allow active devices to be closely spaced.
It is therefore an object of the present invention to provide a method of fabricating totally oxide isolated epitaxial islands.
Therefore, according to the present invention, isolated epitaxial islands are formed by the anodic formation of porous silicon which is then converted to silicon dioxide. The islands are formed by creating a moderately doped island area resting on top of a thin, lightly doped layer. This island area is surrounded by highly doped epitaxial silicon, which is converted to porous silicon by an anodic process. The inclusion of the thin, lightly doped layer underneath the island causes the lower surface of the island to be planar, and improves island definition.
The novel features which characterize the present invention are defined by the appended claims. The foregoing and other objects and advantages of the present invention will hereinafter appear, and for purposes of illustration, but not of limitation, several preferred embodiments are shown in the accompanying drawings.